The behavior of transformed cells differs from that of their normal counterparts in several important aspects. For example: 1. Growth control (i.e. density dependent inhibition of growth; effects of serum on saturation density; and anchorage dependence) is lost, more or less, in transformed cells; 2. lectin-mediated agglutinability is increased in transformed cells; and 3. cell contact phenomena (i.e. contact inhibition of movement; cell adhesion) appear to be significantly altered in transformed cells. In addition, the surface morphology of transformed cells (e.g. the presence of filopodial projections) appears to differ from "normal". All of these differences are thought to involve the macromolecular composition of the cell periphery, and some of these macromolecular constituents can be isolated and chemically characterized. We proposed to isolate and characterize these surface molecules, with particular reference to the role they play in normal cells to regulate contact-inhibition of movement, cell growth, cell agglutinability and cell surface morphology.